By using optical interference method, the authors have studied the process in which a Q-switched YAG laser induced an eye model to break down. It showed that the mechanical effect of the shock results in local discuption of iris. The authors have investigated the plasma shielding in the lipuid eye model, and put forward both the plasma shielding and the focusing angle of the incident laser as two important factors to protect the retina from injury in high-power laser ophthalmology.